1. Technical Field
The present invention relates to an vibrating element, a sensor unit, and an electronic apparatus.
2. Related Art
An vibrating gyro sensor (hereinafter referred to as vibrating gyro) is widely used as an angular velocity sensor that enhances, for example, vehicle-related capabilities, such as vehicle body control and vehicle position detection that is performed by a car navigation system, and optical-apparatus-related capabilities, such as shaking control correction (what is called hand-shake correction) that is performed, for example, by a digital camera and a digital video camcorder. An vibrating gyro includes a gyro vibrating element made of quartz or any other piezoelectric single-crystal material as a highly elastic material, detects an angular velocity in the form of an electric signal produced in part of the gyro vibrating element by swing, rotation, and other vibrating actions of an object of interest, and calculates the angle of rotation to determine the displacement of the object.
As the vibrating element used in a gyro sensor, a piezoelectric vibrating element (vibrating gyro device) made of quartz or any other piezoelectric material has been widely used (see JP-A-5-256723, for example). The vibrating element described in JP-A-5-256723 is what is called a tuning-fork-type piezoelectric vibrating element including a base made of quartz and a pair of vibrating arms extending from one end of the base in parallel to each other. Further, a drive electrode (vibration excitation electrode) is provided on a principal surface (first surface) of each of the vibrating arms, and the drive electrode supplies a drive voltage that causes the vibrating arm to vibrate. A detection electrode is provided on a side surface perpendicular to the first surface of each of the vibrating arms. Each of the vibrating arms is allowed to vibrate when a drive signal (vibration excitation signal) is applied to the drive electrode. When a drive signal is applied to the vibrating element to cause the vibrating arms to vibrate in a direction along the first surface (in-plane vibration), and the vibrating element is rotated around a detection axis extending in the direction in which the vibrating arms extend (for example, Y axis in the case of vibrating gyro device formed of quartz Z plate), the vibrating arms vibrate under a Coriolis force in the direction perpendicular to the first surface (out-of-plane vibration). The amplitude of the out-of-plane vibration, which is proportional to the rotational speed of the vibrating element, can be detected in the form of an angular velocity.
The base and the vibrating arms of the vibrating gyro device described above can be formed as an integral piece by etching quartz or any other suitable piezoelectric material in a photolithography-based process. The vibrating arms are designed to have a rectangular cross-sectional shape, but the actual cross-sectional shape is not a rectangle but is a parallelogram, a rhombus, or a more complicated indefinite shape due to etching anisotropy of quartz, variations in manufacturing processes, and other factors. If the cross-sectional shape of the vibrating arms greatly deviates from an intended rectangular shape, the vibration direction of the vibrating arms deviates from an intended direction, resulting in undesired vibration leakage or what is called a leakage output and causing degradation in detection sensitivity of the vibrating gyro device.
In contrast, JP-A-2010-32482 proposes using a rod-shaped vibrating element having a simple shape and readily processed with precision to form an vibrating element that works as a driver (vibrating arm) and another vibrating element that works as a detector (detection arm) connected to each other. The resultant vibrating element minimizes a leakage output from the detector.
JP-A-2008-209215 proposes a technology for suppressing a leakage output (oblique vibration) from a device formed of a base and vibrating arms extending from the base by setting a portion to be cut in each of the vibrating arms in the vicinity of the base and cutting the portion in laser processing to change the mass distribution of the vibrating arm.
JP-A-2010-32482, however, makes no specific proposal for a method for further suppressing the leakage output based on the configuration in which the two separate vibrating elements, which form the driver and the detector, are connected to each other (specifically, for example, method for further suppressing leakage output resulting from imprecise processing of rod-shaped vibrating element).
On the other hand, the cut portion of the vibrating element described in JP-A-2008-209215 is required to be so small that precise adjustment for leakage output suppression is made. It becomes, however, more difficult in recent years to form such a very small cut portion because an vibrating gyro and hence an vibrating element have been increasingly miniaturized. Further, the formation of the cut portion disadvantageously reduces the mechanical strength of the vibrating element.
To address the problems described above, based on the configuration in which the vibrating arm and the detection arm are formed as two separate vibration portions connected to a base, an adjustment arm for suppressing the leakage output is further separately attached to the base and adjustment is made to suppress the leakage output. Specifically, the mass distribution of the adjustment arm attached to the base is changed, for example, in laser processing to reduce the amount of leakage output. As a result, the amount of leakage output can be reduced without a decrease in mechanical strength of the vibrating element formed of the vibrating arm, the detection arm, and other portions. Newly adding the adjustment arm to the base, however, disadvantageously reduces the detection sensitivity of the vibrating gyro sensor. Specifically, the detection sensitivity can be increased by matching the frequencies of natural vibration of the vibrating arm and the detection arm with each other so that the vibrating arm and the detection arm vibrate in resonance, whereas the newly added adjustment arm causes inconsistency in resonance between the vibrating arm and the detection arm from, disadvantageously resulting in a decrease in detection sensitivity. The problem of a decrease in detection sensitivity occurs not only when an adjustment arm is added to suppress a leakage output but also when any additional portion (protruding portion) is attached to a base.